1. Field of the Invention
This invention relates to bits used for drilling boreholes into the earth for mineral recovery. In particular, the present invention is a bi-center drill bit that can drill a borehole in the earth with a diameter greater than that of the drill bit, and also drill out the cement and float shoe after the casing has been cemented in place.
2. Description of the Related Art
In the pursuit of drilling boreholes into the earth for the recovery of minerals, there are instances when it is desirable to drill a borehole with a diameter larger than the bit itself. Drill bits used to form these boreholes are generally known as bi-center type drill bits.
Bi-center drill bits are well known in the drilling industry. Various types of bi-center drill bits are described in U.S. Pat. Nos. 1,587,266, 1,758,773, 2,074,951, 2,953,354, 3,367,430, 4,408,669, 4,440,244, 4,635,738, 5,040,621, 5,052,503, 5,165,494, 5,678,644 all herein incorporated by reference, and European Patent Application 0,058,061.
Modern bi-center drill bits are typically used in difficult drilling applications where the earth formations are badly fractured, where there is hole swelling, where the borehole has a tendency to become spiraled, or in other situations where an oversize hole is desirable.
In these difficult drilling applications, the top portion of the well bore is often stabilized by setting and cementing casing. The cement, shoe, float, and related cementing hardware are then typically drilled out of the casing by a drill bit that is run into the casing for this purpose. Once the cement and related hardware are drilled out, the drill-out bit is tripped out of the hole and a bi-center drill bit is run back in. Drilling then proceeds with the bi-center drill bit, which drills a hole into the formation below the casing with a diameter that is greater than the inside diameter of the casing.
To reduce drilling expenses, attempts have been made to drill the cement and related hardware out of the casing, and then drill the formation below the casing with a single bi-center drill bit. These attempts often resulted in heavy damage to both the casing and the bi-center drill bit.
The casing tends to be damaged by the gauge cutting elements mounted on the bi-center drill bit because inside the casing the pilot section of the bit is forced to orbit about its center, causing the gauge cutters to engage the casing. The forced orbiting action of the pilot section also causes damage to the cutters on the leading face of the bi-center drill bit.
The degree of damage to both the casing and the bit is further increased when a directional drilling bottom hole assembly is attached to the drill string just above the bit. It is often desirable to directionally drill the borehole beneath the casing with directional drilling systems utilizing bent subs. When the bi-center drill bit drills the cement and related hardware out of the casing with a bent sub directional system, the side forces caused by the forced orbiting action of the bi-center drill bit are additive with the side forces caused by rotating with a bent sub. The resulting complex, and excessive forces have caused failures in bi-center drill bits in as few as three feet of drilling. The same problems occur with related directional drilling systems that force the bi-center drill bits along paths other than their centerlines.
The present invention is a bi-center drill bit designed to drill out the cement and other material in the casing and then proceed to drill out the full gauge drilling diameter borehole with a diameter greater than the inside of the casing. The bi-center drill bit is configured with non-drilling bearing elements that contact with the casing when the bit is drilling the cement without allowing the gauge cutting elements of the bi-center drill bit to contact the casing. The bi-center drill bit also has a cutting element configuration which prevents reverse scraping of the cutting elements when drilling both the cement and the formation.
Disclosed is a bi-center drill bit with a bit body with a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and a reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section, and a first cutting face surface on the pilot section generated by the plurality of cutting elements as they are rotated about the first center of rotation of the pilot section. There is a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D with a second cutting face surface on the pilot section generated by the plurality of cutting elements as they are rotated about the second center of rotation of the pilot section. There is also a first region of the pilot section centered about the first center of rotation having a radius D, a second region of the pilot section centered about the second center of rotation having a radius D and a third region of the pilot section formed by the intersection of the first region and the second region. There are no cutting elements lying within the third region of the pilot section that contact both the first cutting face surface and the second cutting face surface.
Also disclosed is a bi-center drill bit with a bit body, the bit body having a longitudinal axis, a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and an eccentric reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section about the longitudinal axis, and a radius of rotation R1 of the drill bit about the first center of rotation. There is a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D and a radius of rotation R2 of the drill bit about the second center of rotation. The radius of rotation R1 is less than the sum of the radius of rotation R2 and D.
Also disclosed is a bi-center drill bit with a bit body, the bit body having a longitudinal axis, a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and an eccentric reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section about the longitudinal axis, and a radius of rotation R1 of the drill bit about the first center of rotation. There is a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D, and a radius of rotation R2 of the drill bit about the second center of rotation. The radius of rotation R1 is less than the sum of the radius of rotation R2 and D and a plurality of non-cutting bearing elements are mounted upon the bit body at radius R2.
Also disclosed is a bi-center drill bit with a bit body, the bit body having a longitudinal axis, a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and an eccentric reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section about the longitudinal axis, and a radius of rotation R1 of the drill bit about the first center of rotation. There is a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D and a radius of rotation R2 of the drill bit about the second center of rotation. The radius of rotation R1 is less than the sum of the radius of rotation R2 and D and a plurality of gauge cutting elements are mounted upon the bit body at radius R1.
Also disclosed is a bi-center drill bit with a bit body, the bit body having a longitudinal axis, a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and an eccentric reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section about the longitudinal axis, and a radius of rotation R1 of the drill bit about the first center of rotation. There is a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D and a radius of rotation R2 of the drill bit about the second center of rotation. The radius of rotation R1 is less than the sum of the radius of rotation R2 and D and a plurality of non-cutting bearing elements are mounted upon the bit body at radius R2 and a plurality of gauge cutting elements are mounted upon the bit body at radius R1.
Also disclosed is a bi-center drill bit with a bit body with a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body and a reamer section intermediate the first and second ends. There are a plurality of cutting elements on the pilot section, a first center of rotation of the pilot section and a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D. There is a first region of the pilot section centered about the first center of rotation having a radius D, a second region of the pilot section centered about the second center of rotation having a radius D, and a third region of the pilot section formed by the intersection of the first region and the second region. The third region of the pilot section is devoid of cutting elements.
Also disclosed is a bi-center drill bit with a bit body, the bit body having a longitudinal axis, a first end adapted to be detachably secured to a bent sub directional drill tool, a pilot section on a second, opposite end of the bit body and a reamer section intermediate the first and second ends. The outer portion of the pilot section is an uninterrupted circular section.